Boron containing ceramic-aluminum metal composite and method to form the composite

ABSTRACT

A boron containing ceramic-aluminum metal composite is formed by mixing a boron containing ceramic with a metal powder comprised of aluminum or alloy thereof, shaping the mixture into a porous preform, contacting the preform with an infiltrating metal comprised of aluminum or alloy thereof that melts at a lower temperature than the metal powder and heating to a temperature sufficient to melt the infiltrating metal, but insufficient to melt the metal powder, such that the infiltrating metal infiltrates the porous preform to form the composite. The composite that is formed may be used for vehicular parts.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/315,883, filed Aug. 29, 2001.

FIELD OF THE INVENTION

[0002] The invention relates to boron containing ceramic-aluminum metalcomposites. In particular, the invention relates to boroncarbide-aluminum composites.

BACKGROUND OF THE INVENTION

[0003] Aluminum-boron carbide (ABC) composites are of interest forcomponents, such as computer hard drive disks, because of their lowerdensity and higher stiffness than aluminum metal. One of the mostdesirable methods of forming complex shapes of aluminum-boron carbidecomposites has been to infiltrate a boron carbide preform with aluminum.The infiltration method results in a dense ABC composite havingessentially the same geometry and dimensions as the porous preform.

[0004] Unfortunately, because aluminum metal has an aluminum oxidelayer, infiltration has to be performed at a high temperature (i.e.,above 1000° C.). Thus, infiltration has required the use of preformsthat are self-supporting. This has precluded the use of substantialamounts of aluminum in the preform. This is because the preform slumpsand incompletely infiltrates due to melting of the aluminum in thepreform and sintering and reacting with the boron carbide causing thepores to be closed off from the infiltrating metal. Consequently,infiltrated ABC composites have been limited to high boron carbideconcentrations (i.e., at least about 40 percent by volume). The lowerlimit for a self-supporting porous particulate body is generallyconsidered to be 40 percent particulates and the balance pores.

[0005] Other techniques have been used to form ABC composites with highaluminum concentrations, such as solid state sintering and high pressuretechniques below the melting temperature of aluminum. However, sinteringat temperatures below the melting temperature of aluminum suffers fromsintering shrinkages resulting in costly machining and, consequently,only making simple shapes economically viable. Similarly, high pressuretechniques, such as extruding aluminum and boron carbide, are expensiveand limited in the shapes that can be made. In addition, since thealuminum does not melt in these techniques, the bonding between theboron carbide is substantially less compared to when the aluminum meltsand reacts with the boron carbide. Consequently, a composite with lessthan optimal properties is formed by these techniques.

[0006] In addition, boron carbide has been cast in molten aluminum, butsince boron carbide reacts quickly with molten aluminum and decomposesinto boron metal, carbon and water soluble aluminum carbide, the boroncarbide is first encapsulated with a protective metal, such as silver.These techniques suffer from the inability to control detrimental phasesthat reduce strength (e.g., Al₄C₃) in the absence of an additionalexpensive step of coating the boron carbide prior to casting. Thisprotective layer precludes the boron carbide to interfacially bond(react) with the aluminum to make, for example, a stronger composite.

[0007] Accordingly, it would be desirable to provide a material andmethod that overcomes one or more of the problems of the prior art, suchas one of those described above.

SUMMARY OF THE INVENTION

[0008] A first aspect of the invention is a method of forming a boroncontaining ceramic-aluminum metal composite comprising,

[0009] (a) mixing a boron containing ceramic with a metal powdercomprised of aluminum or an aluminum alloy, where the boron containingceramic is reactive with aluminum above the melting temperature ofaluminum,

[0010] (b) shaping the mix of step (a) into a porous preform,

[0011] (c) contacting the porous preform with an infiltrating metalcomprised of aluminum or aluminum alloy having a lower meltingtemperature than the metal powder, and

[0012] (d) heating the porous preform and infiltrating metal to aninfiltrating temperature sufficient to melt the infiltrating metal butinsufficient to melt the metal powder, such that the infiltrating metalinfiltrates the porous preform and forms a substantially dense boroncontaining ceramic-aluminum metal composite.

[0013] Surprisingly, the method is capable of producing, for example, asubstantially dense near net shape boron carbide-aluminum metalcomposite below the melting temperature of pure aluminum (i.e., 660° C.)using infiltration. “Substantially dense” means a body that is at least95 percent of theoretical density. In addition, the method allowsimproved bonding between, for example, boron carbide and aluminum due tothe production of reaction phases between the boron carbide and aluminumin a controlled manner due to the low infiltration temperatures. This inturn allows the production of a novel boron carbide-aluminum body havinga high concentration of aluminum that has improved bonding due to thecontrolled reaction of the lower melting temperature aluminum with boroncarbide.

[0014] A second aspect of the present invention is a boron containingceramic-aluminum metal composite having a density of at least about 95percent of theoretical density and being comprised of at least about 60percent by volume aluminum metal or alloy thereof, with the boroncontaining ceramic and at least one reaction product of the boroncontaining ceramic and aluminum dispersed within the aluminum metal oralloy thereof.

[0015] A third aspect of the present invention is a boron containingceramic-aluminum metal composite having a density of at least about 95percent of theoretical density and being comprised of at least about 30percent by volume aluminum metal or alloy thereof, with the boroncontaining ceramic and at least one reaction product of the boroncontaining ceramic and aluminum dispersed within the aluminum metal oralloy thereof, with the proviso that at most a trace of Al₄C₃ is presentin the composite.

[0016] The ceramic-metal composite may be used in applicationsbenefiting from properties, such as low density and higher stiffnessthan aluminum metal. Examples of components include hard drivecomponents (e.g., E-blocks, suspension arms, disks, bearings, actuators,clamps, spindles, base plates and housing covers); brake components(e.g., brake pads, drums, rotors, housings and pistons); aerospacecomponents (e.g., satellite mirrors, housings, control rods, propellersand fan blades); piston engine components (e.g., valves, exhaust andintake manifolds, cam followers, valve springs, fuel injection nozzles,pistons, cam shafts and cylinder liners) and other structural orrecreational components (e.g., bicycle frames, robot arms, deep seabuoys, baseball bats, golf clubs, tennis rackets and arrows).

DETAILED DESCRIPTION OF THE INVENTION Method for Forming the Composite

[0017] In forming the boron containing ceramic-aluminum metal (BCAM)composite, a boron containing ceramic is mixed with aluminum or alloythereof. The boron containing ceramic is reactive with aluminum abovethe melting temperature of aluminum. Suitable boron containing ceramicsinclude, for example, boron carbide, aluminum boron carbides (e.g.,Al₄BC, Al₃B₄₈C₂ and AlB₂₄C₄) and metal borides (TiB₂, AlB₂, AlB₁₂, SiB₆,SiB₄, and ZrB) and mixtures thereof. Preferably, the boron containingceramic is boron carbide and titanium diboride. Most preferably, theboron containing ceramic is boron carbide.

[0018] The boron containing ceramic may be any morphology (e.g.,particulates, whiskers or fibers), any size and size distributionsuitable to form a porous preform that may be infiltrated. Generally,the boron containing ceramic is comprised of particulates between 0.1 to150 micrometers. Preferably, the particles are at least 0.2 and morepreferably at least about 0.5 micrometer to at most about 100micrometers and more preferably at most about 50 micrometers.

[0019] The metal powder of aluminum or aluminum metal alloy may be anysuitable alloy so long as the powder fails to melt at a temperaturesufficient to infiltrate the infiltrating metal. Since the metal powderand infiltrating metal are comprised of aluminum, they generally will atleast partially form an alloy of aluminum upon infiltration. Preferably,they will form a homogeneous aluminum alloy upon infiltration.

[0020] The metal powder may also be any morphology, size and sizedistribution suitable to form the porous preform. The particular metalpowder selected will be dependent on the final BCAM microstructuredesired. For example, BCAM composites having more uniformmicrostructures are typically produced when the average particle size ofthe boron carbide is larger or equal to the size of the metal powder.Whereas, metal powders having an average particle size larger than theboron carbide generally form BCAM composites with distinctive bi-modalmicrostructures. This is believed to be caused by the formation of poolsof molten aluminum that tend to result in the growth of large binary andternary AlBC phases. Generally, the larger the metal particles arerelative to the boron carbide particles, the larger the reactive productceramic grains are after infiltration and reaction is completed.Finally, mixtures of several metal powder sizes, generally, produceunique networks of larger and smaller, in situ formed, reaction phases.

[0021] Generally, the particle size of the metal powder is from about 1micrometer to about 500 micrometers. Preferably, the particle size ofthe metal powder is at least about 10 micrometers, more preferably atleast about 15 micrometers and most preferably at least about 25micrometers to preferably at most about 300 micrometers, more preferablyat most about 150 micrometers and most preferably at most about 100micrometers.

[0022] The amount of metal powder should be an amount sufficient toallow the infiltrating metal to infiltrate and form a substantiallydense composite. The amount of metal powder, generally, is at leastabout 10 percent by volume to at most about 99 percent by volume of thesolids in the mixture (e.g., solids do not include organics that aresolid at room temperature, for example, “waxes,” which are subsequentlyremoved before infiltrating). Preferably, the amount of metal powder isat least about 15 percent, more preferably at least about 20 percent andmost preferably at least about 25 percent to preferably at most about 40percent, more preferably at most about 80 percent and most preferably atmost about 70 percent.

[0023] The metal powder may be aluminum or an alloy thereof, so long asthe melting temperature is sufficiently higher than the infiltratingmetal to allow formation of a substantially dense composite. Suitablealuminum alloys include those known in the art, such as those describedby 16.80-16.98 of Eschbach's Handbook of Engineering Fundamentals,4^(th) Edition, Ed. B. D. Tapley, John Wiley & Sons, Inc. NY, 1990.Specific examples of alloys include alloys of aluminum that contain oneor more of Cu, Mg, Si, Mn, Cr and Zn. Exemplary aluminum alloys includeAl—Cu, Al—Mg, Al—Si, Al—Mn—Mg and Al—Cu—Mg—Cr—Zn. Specific examples ofaluminum alloys include 6061 alloy, 7075 alloy and 1350 alloy, eachavailable from the Aluminum Company of America, Pittsburgh, Pa.

[0024] The mixing method may be any suitable method, such as those knownin the art. Examples of suitable methods include ball milling, attritionmilling, ribbon blending, vertical screw mixing, V-blending andfluidized zone mixing. Ball milling in a solvent, such as ethanol,heptane, methanol, acetone and other low molecular weight organicsolvents with milling media, such as alumina and boron carbide media,generally provides satisfactory results. Other additives useful in theformation of the porous body from the mixture may be included, such asdispersants, binders and lubricants.

[0025] Any suitable method for shaping the mixture may be used to formthe porous preform. Suitable shaping methods include, for example, slipor pressure casting, pressing and plastic forming methods (e.g.,jiggering, injection molding and extrusion). The forming of the porousbody may include removing, if necessary, solvent and organic additives,such as dispersants, lubricants and binders after shaping of themixture. Each of the above methods and steps are described in moredetail in Introduction to the Principles of Ceramic Processing, J. Reed,J. Wiley and Sons, N.Y., 1988.

[0026] After removal of any organic additives or processing aids, theporous preform may be any density that is still capable of forming theceramic-metal composite, but is generally limited to at least 40 percentof theoretical density (i.e., 60 percent porosity by volume) to 85percent of theoretical density (i.e., 15 percent porosity by volume).The lower limit occurs because bodies with much greater porosity willnot be self supporting. The upper limit is when a substantial amount ofthe pores become closed off and cannot be infiltrated. Preferably, thedensity of the porous body is at least about 45 percent, more preferablyat least about 50 percent, most preferably at least about 60 percent topreferably at most about 80 percent and more preferably at most about 75percent of theoretical density.

[0027] The preform is contacted with an infiltrating metal that isaluminum or alloy thereof. The aluminum or alloy is selected dependingon the metal powder incorporated into the porous preform (i.e., musthave a sufficiently lower melting temperature to form a substantiallydense composite). The infiltrating metal may be any suitable metal, suchas those described for the metal powder. The infiltrating metal may becontacted in any suitable manner, such as placing it upon the preform orplacing it in powder form in a refractory crucible and placing thepreform on top of the infiltrating metal powder.

[0028] The porous preform contacted by the infiltrating metal is heatedto an infiltrating temperature sufficient to melt the infiltratingmetal, but insufficient to melt the metal powder incorporated into thepreform for a time to form a substantially dense boron containingceramic-aluminum metal composite. Generally, the infiltratingtemperature is at least about 10° C. below where melting of the metalpowder occurs. Preferably, the infiltrating temperature is at leastabout 20° C., more preferably at least about 30° and most preferably atleast about 40° C. below where melting of the metal powder occurs.

[0029] It is important to note that melting of the powder may be abovethe melting temperature of the pure aluminum or pure alloy comprisingthe powder, due to the oxide layer on the particles. That is to say, ifthe oxide layer is sufficiently thick, the infiltrating temperature maybe above the melting temperature of a non-oxidized metal powder (i.e.,pure metal). This is so, because the oxide layer may retain the shape ofthe particles and inhibit flow due to melting of the metal. Generally,infiltrating temperatures exceeding the melting temperature of the puremetal of the metal particles are useful for smaller parts. Larger parts,generally, cannot be heated to these higher infiltrating temperaturesbecause of longer infiltration times and greater stresses that can causeslumping due to rupturing of the oxide layers and flow of the metal inthe metal particles. If desired, the aluminum powder may be treated tooptimize the oxide layer, such as heating the powder in an oxygenatmosphere prior to mixing.

[0030] The infiltrating temperature is dependent on the metal powder andinfiltrating metal used, but, generally, is at most about 730° C.Preferably, the infiltrating temperature is at most 700° C., morepreferably at most about 660° C. (about the melting temperature of purealuminum) and most preferably at most about 640° C. It is alsopreferable that the infiltrating temperature is below the meltingtemperature of the metal powder without a metal oxide layer (i.e., puremetal). Preferably, the infiltrating temperature is at least about 10°C., more preferably at least about 20° and most preferably at leastabout 40° C. below the melting temperature of the pure metal of themetal powder used. The time at the infiltrating temperature may be anysuitable time to form the composite. Generally, the time is from about aminute to 24 hours. Preferably, the time is several minutes to severalhours.

[0031] Heating may be performed under any suitable atmosphere. Forexample, heating may be performed in inert atmospheres (e.g., noblegases or mixtures thereof) at atmospheric pressures or under vacuum.Preferably, the heating is performed under vacuum or inert atmospheresat a pressure less than or equal to atmospheric pressure. Morepreferably, the heating is performed under a vacuum.

[0032] It has also been discovered that after forming the substantiallydense BCAM composite, the BCAM composite may be further heated to atemperature exceeding the melt temperature of the metal powder withoutslumping or distortion of the dense BCAM composite. This further heattreatment improves the bonding (reaction) between the starting ceramicand aluminum metal in the composite, increasing, for example, thestrength of the BCAM composite. However, this further heat treatmenttemperature must not be so great or for an extended time that the BCAMcomposite distorts or slumps or the ceramic decomposes or formsdeleterious phases (e.g., aluminum carbide). Thus, it should beunderstood that this further heat-treatment temperature may besubstantially higher than the melting temperature of the metal powder,so long as the time is short. For example, if the heat treatment is to atemperature of 1025° C., the time must be very short, such as less thanabout 10 minutes. In contrast, if the temperature is just above wherethe pure metal of the metal powder begins to melt, the time attemperature may be for several hours.

The BCAM Composite

[0033] To reiterate, the BCAM composite that is formed by the method issubstantially dense, which means it is at least 95 percent oftheoretical density. Preferably, the composite is at least about 97percent, more preferably at least 98 percent, even more preferably atleast about 99 percent and most preferably essentially 100 percent oftheoretical density.

[0034] The BCAM is comprised of a metal matrix that is an aluminum alloywith a boron containing ceramic (starting ceramic powder used to makethe preform) and at least one reaction phase that is a reaction productof the boron containing ceramic and aluminum. As an illustration, whenthe boron containing ceramic is boron carbide, the composite willcontain boron carbide, aluminum alloy and a reaction phase, such asAlB₂, Al₄BC, Al₃B₄₈C₂, AlB₁₂, Al₄C₃ and AlB₂₄C₄. In this embodiment,Al₄C₃ is preferably present in at most a trace amount and morepreferably not at all.

[0035] The amount of metal in the BCAM composite is at least about 30percent by volume to at most about 98 percent by volume when there is atmost a trace amount of Al₄C₃. Preferably, the amount of metal is atleast about 40 percent, more preferably at least about 50 percent andmost preferably at least about 60 percent to preferably at most about 95percent, more preferably at most about 90 percent and most preferably atmost about 85 percent by volume of the composite. The balance of thecomposite is the initial boron containing ceramic phase and the reactionproduct.

[0036] The amount of metal in the BCAM composite is at least about 60percent by volume to at most about 98 percent by volume when there ismore than a trace amount of Al₄C₃. Preferably, the amount of metal is atleast about 65 percent, more preferably at least about 70 percent andmost preferably at least about 75 percent to preferably at most about 95percent, more preferably at most about 90 percent and most preferably atmost about 85 percent by volume of the composite. The balance of thecomposite is the initial boron containing ceramic phase and the reactionproduct.

[0037] It is preferred that at least 10 percent by volume of the boroncontaining ceramic used to make the porous preform is present in theBCAM composite. That is to say, at least 10 percent of the boroncontaining ceramic has not reacted to form the reaction product.Preferably, at least 50 percent, more preferably at least 75 percent,even more preferably at least 80 percent and most preferably at least 85percent by volume to preferably at most about 99 percent of the boroncontaining ceramic is present in the BCAM composite. That is to say, theamount of ceramic (i.e., boron containing ceramic and reaction product)in the composite is comprised of at least 10 percent by volume of theboron containing ceramic.

[0038] The boron containing ceramic-aluminum metal composite of thepresent invention has improved bonding resulting in a composite that isboth light weight and stiffer than aluminum, while retaining much, ifnot all, of the toughness of aluminum. Because of this, the composite isparticularly useful for vehicular parts. “Vehicular” means any motorizedwheeled transportation device, such as a bicycle, motorcycle,automobile, truck, bus, airplane and train. Parts include but are notlimited to brake part, suspension part, body part, steering part, wheelrim, engine part, coolant or heating system part, air conditioning part,fuel part, exhaust part, transmission part, clutch part or drive axlepart.

EXAMPLES

[0039] For each of the examples, the strength was determined usingMIL-STD-1942b standard. The hardness was determined using Vickersindentation. The Young's modulus was determined by using a digitaloscilloscope, Tektronix model 2430A, Tektronix Inc., Beaverton, Oreg.The density was determined by Autopycnometer 1320, Fisher Scientific,Pittsburgh, Pa. The phases present in the composite were determined byx-ray diffraction using an x-ray diffractometer using CuK_(alpha)radiation and a scan rate of 2 degrees per minute.

Example 1

[0040] Fifty parts by weight of boron carbide (B₄C, obtained fromElectrosmeltzwerk Kempton “ESK”, Kempton, Germany, were dry mixed with50 parts by weight of a high purity aluminum powder (Series 1100, Alcoa,Pittsburgh, Pa.). The boron carbide had an average particle size ofabout 10 micrometers. The aluminum powder had an average particle sizeof about 40 micrometers. The aluminum powder had a melt temperature ofabout 660° C. The mixed powders were pressed in one-inch diameter die toform a porous preform having a density of about 50 percent oftheoretical. The preform was placed in an alumina crucible. Solid piecesof 6061 aluminum alloy (available from Alcoa, Pittsburgh, Pa.) wereplaced on top of the preform. The 6061 aluminum alloy melts from about580° to 610° C. The crucible was heated to 620° C. for 15 minutes andcooled. The resultant composite had a density greater than 98 percent oftheoretical density. The composite contained, by volume, about 73percent aluminum alloy, 23 percent boron carbide and 4 percent reactionphases of aluminum boron carbides. The composite had a strength of 220MPa, hardness of 350 Kg/mm² and elastic modulus (Young's modulus) of 65GPa.

Example 2

[0041] A composite was prepared in the same manner as in Example 1,except that after heating to 620° C. the temperature was increased to640° C. for 1 hour prior to cooling. The composite had a density of atleast 98 percent of theoretical density. The composite contained, byvolume, 65 percent aluminum alloy, 20 percent boron carbide and 15percent aluminum boron carbide phases. The composite had a strength of200 MPa, hardness of 500 Kg/mm² and Young's modulus of 70 GPa.

Example 3

[0042] A composite was prepared in the same manner as in Example 2,except that after heating to 640° C. the furnace was heated to 1025° C.for 5 minutes prior to cooling. The composite had a density of at least98 percent of theoretical density. The composite contained, by volume,about 67 percent by volume aluminum alloy, 16 percent boron carbide and17 percent aluminum boron carbide phases. The composite had a strengthof 450 MPa, hardness of about 550 Kg/mm² and Young's modulus of about150 GPa.

Comparative Example 1

[0043] A preform was made in the same manner as Example 1, except thepreform was made solely from the boron carbide powder (i.e., no metalpowder). The preform was placed in an alumina crucible and the samealuminum alloy placed on top of the preform as in Example 1. The heatingwas also the same as in Example 1. The preform was not infiltrated bythe aluminum alloy.

What is claimed is:
 1. A method of forming a boron containingceramic-aluminum metal composite comprising, (a) mixing a boroncontaining ceramic with a metal powder comprised of aluminum or analuminum alloy, where the boron containing ceramic is reactive withaluminum above the melting temperature of aluminum, (b) shaping the mixof step (a) into a porous preform, (c) contacting the porous preformwith an infiltrating metal comprised of aluminum or aluminum alloyhaving a lower melting temperature than the metal powder, and (d)heating the porous preform and infiltrating metal to an infiltratingtemperature sufficient to melt the infiltrating metal but insufficientto melt the metal powder, such that the infiltrating metal infiltratesthe porous preform and forms a substantially dense boron containingceramic-aluminum metal composite.
 2. The method of claim 1 wherein theboron containing ceramic-aluminum metal composite is comprised of atleast one reaction product of the boron containing ceramic and aluminum.3. The method of claim 2 wherein the boron containing ceramic is boroncarbide.
 4. The method of claim 3 wherein the reaction product iscomprised of AlB₂, Al₄BC, Al₃B₄₈C₂, AlB₁₂, Al₄C₃, AlB₂₄C₄ or mixturesthereof.
 5. The method of claim 4 wherein the reaction product iscomprised of AlB₂, Al₄BC, Al₃B₄₈C₂, AlB₁₂, AlB₂₄C₄ or mixtures thereof6. The method of claim 1 wherein at least 60 percent by volume of theboron containing ceramic-aluminum metal composite is aluminum or alloythereof.
 7. The method of claim 5 wherein at least 70 percent by volumeof the boron containing ceramic-aluminum metal composite is aluminum oralloy thereof.
 8. The method of claim 1 wherein the infiltratingtemperature is at least 10° C. below the temperature where the metalpowder melts.
 9. The method of claim 8 wherein the infiltratingtemperature is at least about 20° C. below the temperature where themetal powder melts.
 10. The method of claim 1 wherein the boroncontaining ceramic-metal composite is further heated to a heat-treatmenttemperature in excess of a temperature where the metal powder melts. 11.A boron containing ceramic-aluminum metal composite having a density ofat least 95 percent of theoretical density and being comprised of atleast 60 percent by volume aluminum metal or alloy thereof, with theboron containing ceramic and at least one reaction product of the boroncontaining ceramic and aluminum dispersed within the aluminum metal oralloy thereof.
 12. The boron containing ceramic aluminum metal compositewherein the composite is comprised of at least 70 percent by volumealuminum or alloy thereof.
 13. The composite of claim 11 wherein theboron containing ceramic is boron carbide and the reaction product iscomprised of AlB₂, Al₄BC, Al₃B₄₈C₂, AlB₁₂, Al₄C₃, AlB₂₄C₄ or mixturesthereof.
 14. The composite of claim 13 wherein the reaction product isAlB₂, Al₄BC, Al₃B₄₈C₂, AlB₁₂, AlB₂₄C₄ or mixtures thereof.
 15. Thecomposite of claim 13 wherein the boron containing ceramic is present inthe composite in an amount of at least 10 percent by volume of the totalamount of boron containing ceramic and reaction product present in thecomposite.
 16. The composite of claim 15 wherein the amount of boroncontaining ceramic is at least 50 percent by volume of the total amountof boron containing ceramic and reaction product present in thecomposite.
 17. The composite of claim 16 wherein the amount of the boroncontaining ceramic is at least 75 percent by volume of the total amountof boron containing ceramic and reaction product present in thecomposite.
 18. A vehicular part comprised of the composite of claim 11.19. The part of claim 18 wherein the vehicular part is a brake part,suspension part, body part, steering part, wheel rim, engine part,coolant or heating system part, air conditioning part, fuel part,exhaust part, transmission part, clutch part or drive axle part.
 20. Aboron containing ceramic-aluminum metal composite having a density of atleast about 95 percent of theoretical density and being comprised of atleast about 30 percent by volume aluminum metal or alloy thereof, withthe boron containing ceramic and at least one reaction product of theboron containing ceramic and aluminum dispersed within the aluminummetal or alloy thereof, with the proviso that at most a trace of Al₄C₃is present in the composite.
 21. The composite of claim 20 wherein thereaction product is AlB₂, Al₄BC, Al₃B₄₈C₂, AlB₁₂, AlB₂₄C₄ or mixturesthereof.
 22. The composite of claim 20 wherein the boron containingceramic is present in the composite in an amount of at least 10 percentby volume of the total amount of boron containing ceramic and reactionproduct present in the composite.
 23. The composite of claim 20 whereinthe amount of boron containing ceramic is at least 50 percent by volumeof the total amount of boron containing ceramic and reaction productpresent in the composite.
 24. The composite of claim 23 wherein theamount of the boron containing ceramic is at least 75 percent by volumeof the total amount of boron containing ceramic and reaction productpresent in the composite.
 25. A vehicular part comprised of thecomposite of claim
 20. 26. The part of claim 25 wherein the vehicularpart is a brake part, suspension part, body part, steering part, wheelrim, engine part, coolant or heating system part, air conditioning part,fuel part, exhaust part, transmission part, clutch part or drive axlepart.